The present invention relates to a fuel cell having an electrolyte membrane sandwiched between an anode electrode and a cathode electrode.
Solid polymer electrolyte fuel cells comprise a plurality of stacked fuel cell structural bodies (unit cells) each comprising an electrolyte membrane in the form of an ion exchange membrane and a catalytic electrode and a porous carbon electrode which are disposed one on each side of the electrolyte membrane, and a plurality of separators sandwiching the structural bodies.
Hydrogen supplied to the anode of the fuel cell is converted into hydrogen ions on the catalytic electrode, which move through the electrolyte membrane that has been humidified to an appropriate extent toward the cathode of the fuel cell. Electrons generated while the hydrogen ions are moving are transferred to an external circuit for use as direct-current electric energy. An oxygen containing gas such as an oxygen gas or air is supplied to the cathode electrode to generate water through a reaction between the hydrogen ions, the electrons, and the oxygen on the cathode electrode.
For such a fuel cell, there has been known a structure which, as shown in FIG. 11 of the accompanying drawings, comprises fuel cell structural bodies 2 and separators 4 which are alternately stacked together, each of the fuel cell structural bodies 2 having an electric generation section (electrode) 2a which is supplied with cooling water in a direction parallel to the flow of a fuel gas, e.g., a hydrogen gas and an oxygen containing gas, e.g., an oxygen gas.
Since the cooling water flows vertically in the electric generation section 2a, a relatively large temperature difference is developed between central and opposite side regions of the electric generation section 2a due to thermal diffusion. Because of a drop in the temperature, moisture is condensed in the opposite side regions of the electric generation section 2a, creating inoperative regions in the electric generation section 2a. In addition, the electric generation section 2a tends to have low-performance regions on account of the low temperature. As a result, the electric generation section 2a has its effective operative area and performance greatly lowered.
It is an object of the present invention to provide a fuel cell which will solve the above problems and has a simple structure for preventing partial temperature differences from being developed in fuel cell structural bodies thereby to maintain an effective operative area and performance.
According to the present invention, a cooling medium, which has been used to cool an electric generation section of a fuel cell structural body, is then circulated along outer sides of the electric generation section. Therefore, the cooling medium whose temperature has been increased by a heat exchange in the electric generation section flows outside of the electric generation section. Consequently, any temperature difference between a central region of the electric generation section and outer edges thereof is minimized, thereby preventing moisture condensation and increasing an effective operative area and the performance of the electric generation section.